If you have 2 hard disks or use PartitionMagic to create 2 active boot partitions you can install 98 on one and Me on the other. However, when booting into the other OS you must mark the other OS's partition as hidden. Only 1 can be active at a time.
Simply put just pick either ME or 98, 98 is nearly dead, ME while it isn't the best of the 9x OSes, it'll be supported (games and stuff) for at least as long as Windows 2000 is around.